Organic light emitting display

ABSTRACT

An organic light emitting display is capable of reducing variation in power transmitted to pixels to reduce or prevent non-uniformity of brightness from being generated. The organic light emitting display includes a pixel including a red sub pixel, a green sub pixel, and a blue sub pixel and first pixel power source lines for supplying a first pixel power from a first pixel power source to the red sub pixel, the green sub pixel, and the blue sub pixel, wherein the first pixel power source lines coupled to at least two different color sub pixels of the red, green and blue sub pixels have different widths. The first pixel power source lines have widths that may correspond to a voltage drop of the first pixel power source or may correspond to deterioration of the respective sub pixels to which they are coupled.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2010-0040043, filed on Apr. 29, 2010, in the KoreanIntellectual Property Office, the entire content of which isincorporated herein by reference.

BACKGROUND

1. Field

An embodiment of the present invention relates to an organic lightemitting display.

2. Description of Related Art

Recently, various flat panel displays (FPDs) capable of reducing weightand volume, which are disadvantages of cathode ray tubes (CRTs), havebeen developed. The FPDs include liquid crystal displays (LCDs), fieldemission displays (FEDs), plasma display panels (PDPs), and organiclight emitting displays.

Among the FPDs, the organic light emitting display displays an imageusing organic light emitting diodes (OLEDs) that generate light by therecombination of electrons and holes.

The organic light emitting displays are being widely applied in personaldigital assistants (PDAs), MP3 players, and mobile telephones due toadvantages such as excellent color reproducibility and reducedthickness.

FIG. 1 is a circuit diagram illustrating a pixel of an organic lightemitting display. Referring to FIG. 1, the pixel is coupled to a dataline Dm, a scan line Sn, and a pixel power source line coupled to apixel power source ELVDD and includes a first transistor M1, a secondtransistor M2, a capacitor Cst, and an organic light emitting diodeOLED.

In the first transistor M1, a source is coupled to the pixel powersource line ELVDD, a drain is coupled to the OLED, and a gate is coupledto a first node N1. In the second transistor M2, a source is coupled tothe data line Dm, a drain is coupled to the first node N1, and a gate iscoupled to the scan line Sn. The capacitor Cst is coupled between thefirst node N1 and the pixel power source ELVDD to maintain a voltagebetween the first node N1 and the pixel power source ELVDD for an amountof time (e.g., a predetermined time). The OLED includes an anodeelectrode, a cathode electrode, and a light emitting layer. In the OLED,the anode electrode is coupled to the drain of the first transistor M1and the cathode electrode is coupled to a low potential power sourceELVSS, so that when current flows from the anode electrode to thecathode electrode, the light emitting layer emits light, and brightnessis controlled corresponding to the amount of current.

In the pixel having the above structure, current corresponding toEQUATION 1 flows to the OLED.

$\begin{matrix}{I_{d} = {\frac{\beta}{2}\left( {{Vgs} - {Vth}} \right)^{2 =}\frac{\beta}{2}\left( {{ELVdd} - {Vdata} - {Vth}} \right)^{2}}} & {{EQUATION}\mspace{14mu} 1}\end{matrix}$

wherein, I_(d), Vgs, Vth, ELVdd, Vdata, and β represent current thatflows to the OLED, a voltage between the gate and source of the firsttransistor, a threshold voltage of the first transistor, a voltage ofthe pixel power source, a voltage of the data signal, and a constant,respectively.

Since the current that flows to the OLED is as represented by EQUATION1, when the voltage of the pixel power source ELVDD changes, the amountof current that flows also changes.

Therefore, since a magnitude of internal resistance of the pixel powersource line to which the pixel power source ELVDD is coupled varies witha distance of the pixel from the pixel power source ELVDD, a differencein brightness between pixels may be generated.

SUMMARY

Accordingly, embodiments of the present invention have been made toprovide an organic light emitting display capable of reducing variationsin power transmitted to pixels to reduce or prevent non-uniformity ofpixel brightness.

In order to achieve the foregoing and/or other aspects of the presentinvention, according to a first aspect of the present invention, thereis provided an organic light emitting display including a pixelincluding a red sub pixel, a green sub pixel, and a blue sub pixel andfirst pixel power source lines for supplying a first pixel power from afirst pixel power source to the red sub pixel, the green sub pixel, andthe blue sub pixel, wherein the first pixel power source lines coupledto at least two different color sub pixels of the red, green and bluesub pixels have different widths.

The widths of the first pixel power source lines may correspond to avoltage drop of the first pixel power source.

The widths of the first pixel power source lines may correspond todeterioration of the respective sub pixels to which they are coupled.

The first pixel power source lines coupled to the blue sub pixels mayhave a largest width among the first pixel power source lines.

The organic light emitting display may further include a data driver fortransmitting data signals to the pixel and a scan driver fortransmitting scan signals to the pixel.

The first pixel power source lines coupled to the green sub pixels mayhave a smallest width among the first pixel power source lines.

The first pixel power source lines may include a first main pixel powersource line electrically coupled to a first sub pixel power source line.

In the organic light emitting display according to embodiments of thepresent invention, variation in the power transmitted to pixels isreduced to reduce or prevent non-uniformity of pixel brightness. Inaddition, a change in an aperture ratio is reduced, making it possibleto reduce or prevent brightness deterioration.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustrateexemplary embodiments of the present invention, and, together with thedescription, serve to explain the principles of embodiments of thepresent invention, wherein:

FIG. 1 is a circuit diagram illustrating a pixel of an organic lightemitting display;

FIG. 2 is a schematic diagram illustrating an organic light emittingdisplay according to an embodiment of the present invention;

FIG. 3A is a graph illustrating the current error ratios of a red subpixel, a green sub pixel, and a blue sub pixel, which are caused by theinternal resistance of first pixel power source lines;

FIG. 3B is a graph illustrating the voltage drops of the red sub pixel,the green sub pixel, and the blue sub pixel, which are caused by theinternal resistance of the first pixel power source lines; and

FIG. 4 is a layout diagram illustrating the pixel of the embodimentshown in FIG. 2.

DETAILED DESCRIPTION

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature and not restrictive. In addition, when anelement is referred to as being “on” another element, it can be directlyon the element or be indirectly on the element with one or moreintervening elements interposed therebetween. Also, when an element isreferred to as being “connected to” or “coupled to” another element, itcan be directly connected to the element or be indirectly connected tothe element with one or more intervening elements interposedtherebetween. Hereinafter, like reference numerals refer to likeelements.

Hereinafter, embodiments of the present invention will be described asfollows with reference to the attached drawings.

FIG. 2 is a schematic diagram illustrating an organic light emittingdisplay according to an embodiment of the present invention. FIG. 3A isa graph illustrating current error ratios of a red sub pixel, a greensub pixel, and a blue sub pixel, which are caused by internal resistanceof first pixel power source lines. FIG. 3B is a graph illustratingvoltage drops of the red sub pixel, the green sub pixel, and the bluesub pixel, which are caused by the internal resistance of the firstpixel power source lines.

Referring to FIG. 2, the organic light emitting display includes adisplay unit 100, a data driver 200, and a scan driver 300. The displayunit 100 includes a plurality of data lines D1, D2, . . . , Dm-1, andDm, a plurality of scan lines Si, S2, . . . , Sn-1, and Sn, and aplurality of pixels 101 formed in regions defined by the plurality ofdata lines D1, D2, . . . , Dm-1, and Dm and the n scan lines S1, S2,Sn-1, and Sn. In addition, each of the pixels 101 receives power from afirst pixel power source ELVDD and a second pixel power source ELVSS tobe driven. At this time, the power from the first pixel power sourceELVDD is received (e.g., commonly received) through a plurality of firstpixel power source lines and the power from the second pixel powersource ELVSS is received (e.g., commonly received) through an electrodedeposited on the front surface of the display unit.

Each pixel 101 includes a red sub pixel, a green sub pixel, and a bluesub pixel. In addition, each of the sub pixels includes a pixel circuitand an organic light emitting diode (OLED), and generates pixel currentthat flows from the pixel circuit to the pixel corresponding to datasignals transmitted through the plurality of data lines D1, D2, . . . ,Dm-1, and Dm and scan signals transmitted through the plurality of scanlines S1, S2, . . . , Sn-1, and Sn, so that the pixel current flows tothe OLED.

At this time, as illustrated in FIGS. 3A and 3B, the current errorratios and the voltage drops of a red sub pixel, a green sub pixel, anda blue sub pixel, which are caused by the internal resistance of thefirst pixel power source lines being different from each other, areshown. For example, the current error ratio of the blue sub pixel is 7%,the current error ratio of the red sub pixel is 4.9%, and the currenterror ratio of the green sub pixel is 4.4%. In addition, the voltagedrop of the green sub pixel is 94 mV, the voltage drop of the red subpixel is 47 mV, and the voltage drop of the green sub pixel is 35 mV.The current error ratio and voltage drop of the blue sub pixel arelarger than the current error ratios and voltage drops of the red subpixel and the green sub pixel. Therefore, the non-uniformity ofbrightness of the blue sub pixel is larger than the non-uniformity ofbrightness of the other two sub pixels. A width of the first pixel powersource lines may be increased to reduce the current error ratios andvoltage drops of the first pixel power source lines. However, when thewidth of the first pixel power source lines is increased as if all ofthe first pixel power source lines are coupled to blue sub pixels, thewidths of the first pixel power source lines coupled to red sub pixelsand green sub pixels are unnecessarily large, and an aperture ratio isreduced.

Therefore, according to an embodiment of the present invention, widthsof the first pixel power source lines of the sub pixels vary. That is,the thicknesses (or widths) of the first pixel power source linescoupled to the red sub pixel, the green sub pixel, and the blue subpixel vary (e.g., are independently set) so that the width of the firstpixel power source line coupled to the red sub pixel is determined inaccordance with the voltage drop and current error ratio of the red subpixel, and the width of the first pixel power source line coupled to thegreen sub pixel is determined in accordance with the voltage drop andcurrent error ratio of the green sub pixel. In addition, the width ofthe first pixel power source line coupled to the blue sub pixel isdetermined in accordance with the voltage drop and current error ratioof the blue sub pixel.

The data driver 200 is coupled to the m data lines D1, D2, . . . , Dm-1,and Dm and generates data signals to sequentially transmit the datasignals row-by-row to the m data lines D1, D2, . . . , Dm-1, and Dm(e.g., to the data lines one row at a time).

The scan driver 300 is coupled to the n scan lines S1, S2, . . . , Sn-1,and Sn and generates scan signals to transmit the scan signals to the nscan lines S1, S2, . . . , Sn-1, and Sn. A specific row (e.g., aspecific scan line) is selected by the scan signals and the data signalsare transmitted to the pixels 101 positioned in the selected row so thatcurrents corresponding to the data signals are generated in the pixels.

FIG. 4 is a layout diagram illustrating the pixel of the embodimentshown in FIG. 2. Referring to FIG. 4, the pixel includes a red sub pixel120R, a green sub pixel 120G, and a blue sub pixel 120B.

Each of the red sub pixel 120R, the green sub pixel 120G, and the bluesub pixel 120B includes a transistor Tr and a storage capacitor Cst. Thered sub pixel 120R, the green sub pixel 120G, and the blue sub pixel120B are coupled to the scan line Sn and the data line Dm, and arecoupled to first pixel power source lines, e.g., a first pixel powersource line ELVDDR for supplying the first pixel power source ELVDD tothe red sub pixel 120R, a first pixel power source line ELVDDG forsupplying the first pixel power source ELVDD to the green sub pixel120G, and a first pixel power source line ELVDDB for supplying the firstpixel power source ELVDD to the blue sub pixel 120B.

At this time, as illustrated in FIGS. 3A and 3B, since the voltage dropand the current error rate generated by the first pixel power sourceline ELVDDB coupled to the blue sub pixel 120B are largest, and sincethe voltage drop and the current error rate generated by the first pixelpower source line ELVDDG coupled to the green sub pixel 120G aresmallest, the width of the first pixel power source line ELVDDB coupledto the blue sub pixel 120B is largest, and the width of the first pixelpower source line ELVDDG coupled to the green sub pixel 120G issmallest.

As described above, when the width of the first pixel power source linesis determined in accordance with the voltage drops and current errorratios of the respective sub pixels to which the first pixel powersource lines are coupled, the sum of the widths of all of the firstpixel power source lines is smaller than if the width of all of thefirst pixel power source lines were determined in accordance with onlythe sub pixel whose efficiency is lowest.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but, on the contrary, isintended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of the appended claims, andequivalents thereof.

1. An organic light emitting display, comprising: a pixel comprising ared sub pixel, a green sub pixel, and a blue sub pixel; and first pixelpower source lines for supplying a first pixel power from a first pixelpower source to the red sub pixel, the green sub pixel, and the blue subpixel, wherein the first pixel power source lines coupled to at leasttwo different color sub pixels of the red, green and blue sub pixelshave different widths.
 2. The organic light emitting display as claimedin claim 1, wherein the widths of the first pixel power source lines arein accordance with voltage drop of the first pixel power source.
 3. Theorganic light emitting display as claimed in claim 1, wherein the widthsof the first pixel power source lines correspond to deterioration of therespective sub pixels to which they are coupled.
 4. The organic lightemitting display as claimed in claim 1, wherein the first pixel powersource lines coupled to the blue sub pixels have a largest width amongthe first pixel power source lines.
 5. The organic light emittingdisplay as claimed in claim 1, further comprising: a data driver fortransmitting data signals to the pixel; and a scan driver fortransmitting scan signals to the pixel.
 6. The organic light emittingdisplay as claimed in claim 1, wherein the first pixel power sourcelines coupled to the green sub pixels have a smallest width among thefirst pixel power source lines.
 7. The organic light emitting display asclaimed in claim 1, wherein the first pixel power source lines comprisea first main pixel power source line electrically coupled to a first subpixel power source line.
 8. An organic light emitting displaycomprising: a plurality of pixels, each of the pixels comprising a redsub pixel, a green sub pixel, and a blue sub pixel; a data driver fortransmitting data signals to the pixels; and a plurality of power linescoupled to the sub pixels, wherein the width of the power lines coupledto the blue sub pixels are larger than the width of the power linescoupled to the red and green sub pixels.
 9. The organic light emittingdisplay as claimed in claim 8, wherein the width of the power linescoupled to the green sub pixels are smaller than the width of the powerlines coupled to the red sub pixels.